Keeping snakes OUT is the key...Let the possums eat them...Those that are outside will help control rats & mice that are smaller ....Hardware cloth is the Fix that works....3' high....cant climb it or get throughMaybe you need to figure out where the snake den is located. That many snakes usually mean's that they have a den nearby and are breeding. Just turning them loose outside of your coop isn't going to make them magically go away. They know where the food is at, and will return. I had to deal with one ratsnake early last fall.